1. Background of the Invention
Tuning-fork type resonators are especially used as reference sources for clocks, and are built into not only watches but also electronic equipment such as portable telephones, digital cameras, and the like as parts providing a clock function. In recent years, as such electronic equipment has become widespread and small sized, tuning-fork type resonators have also been formed by etching using photolithography.
2. Prior Art
FIG. 4 is a plan view of an example of a conventional tuning-fork type resonator, viewed with its lid removed. Furthermore, FIG. 5A and FIG. 5B are diagrams of the tuning-fork type resonator described in detail. In particular, FIG. 5A is a perspective view of the tuning-fork type resonator, including the electrode wiring, and FIG. 5B is a cross-sectional diagram showing a cross-section through line A-A of FIG. 5A with an oscillator circuit.
As shown in FIG. 4, the example of a conventional tuning-fork type resonator is provided with a tuning fork shaped quartz crystal piece 3 with a pair of tuning fork arms 2a and 2b extending from a tuning fork base 1. The two tuning fork arms 2a and 2b have excitation electrodes 4 on each of their four surfaces excluding the distal end surfaces (head surfaces). As shown in FIG. 5B, all of the excitation electrodes 4 are connected. That is, they are connected such that the electric potentials between each of the two main surfaces and between each of the two side surfaces in the respective tuning fork arms 2a and 2b are the same, those between the two side surfaces and the two main surfaces are reversed, and the electric potentials between the two main surfaces and between the two side surfaces of the tuning fork arms 2a and 2b are reversed relative to each other.
Excitation electrodes 4 with the same potentials are connected together, and as shown in FIG. 5A, a pair of electrodes extends to the bottom of the main surfaces of the tuning fork base 1. Normally, as shown in FIG. 4, metal films 5a and 5b for frequency adjustment are formed on the main surfaces on the tip sides of the tuning fork arms 2a and 2b. Then these, including the excitation electrodes 4 and the like are outline machined by etching using photolithography, for example, and many tuning fork shaped quartz crystal pieces 3 are connected integrally on a quartz crystal wafer 9 as shown in FIG. 2, which is described later.
After being divided into individual tuning-fork shaped quartz crystal pieces from the quartz crystal wafer 9 as shown in FIG. 2, the bottom of the main surface of the tuning fork base 1 of a tuning-fork shaped quartz crystal piece 3 is fixed to inner wall pad sections 7 at one end of a surface mount housing (enclosure) 6 having a concave cross-section, which provides terminals to the quartz crystal, and is connected electrically and mechanically. The open end surface of the surface mount housing (enclosure) 6 is sealed by a lid (not shown in the figure), and the tuning-fork shaped quartz crystal piece 3 is sealed in. Normally, this is a vacuum seal, which limits the increase in crystal impedance (CI) caused by miniaturization.
With this device, in a state in which the tuning-fork shaped quartz crystal pieces 3 are connected integrally on the quartz crystal wafer 9, parts of the metal films 5a and 5b on the main surfaces of the tips are removed by melting and dispersing using a laser such as a YAG or the like. Then, the oscillation frequencies of the tuning-fork type resonators (tuning-fork shaped quartz crystal pieces 3) are adjusted from low to high. In this case, since the frequency of the tuning-fork type resonators can be adjusted at a quartz crystal wafer level collectively, it is possible to increase the productivity.
Alternatively, the frequency of the tuning-fork type resonator may be adjusted by removing parts of the metal films 5a and 5b, similarly, after the tuning-fork shaped quartz crystal piece 3 is housed in the surface mount housing (enclosure) 6. In this case, the oscillation frequency at room temperature can be adjusted within the specification allowing for the change in the oscillation frequency when the tuning fork base 1 is fixed on the pad sections 7. Furthermore, it is also possible to adjust the oscillation frequency finely after adjusting the oscillation frequency of each of the tuning-fork shaped crystal pieces 3 roughly in a quartz crystal wafer 9 state, and separating them into individual pieces to be housed in the surface mount housings (enclosures) 6.
Moreover, there is another method in which characteristic adjustment is performed by gradually cutting off the outer corners of the oscillation arm parts of the tuning-fork type quartz crystal piece using a laser light with a wavelength suitable for cutting quartz crystal.
(Refer to Japanese Unexamined Patent Publication No. 2004-201105, Japanese Unexamined Patent Publication No. 2004-289237, Japanese Unexamined Patent Publication No. 2007-57411, and Japanese Unexamined Patent Publication No. 2000-278066)